Annoying indentation behaviour when declaring data types

[jstolarek]

Say I have this code:

foo = undefinedX

where X is the cursor position. If I press Enter twice the cursor ends up at the beginning of a new line:

foo = undefined

X

This is all fine. Now consider a similar situation with data type declaration:

data Foo = Bar
         | BazX

Now pressing Enter twice yields:

data Foo = Bar
         | Baz

           X

This is mostly annoying. If I press Enter twice after a data constructor declaration then I almost certainly want to start some new declaration and thus expect the cursor to be placed at the beginning of a new line. So the rule should be: when pressing enter on a line that contains only whitespace characters place the cursor at the beginning of a new line. Note also that current behaviour is inconsistent:

data Foo = BarX

Pressing Enter here will place the cursor at the beginning of a new line, but I would really expect it to be placed under =:

data Foo = Bar
         X

Only when I press enter for the second time I want the cursor to be placed at the beginning of a new line.

[gracjan]

I'm really grateful for these reports. Keep those coming. We will fix as soon as possible. Thanks again.

[jstolarek]

I thought a bit more about this and I think that pressing Enter in this situation:

data Foo = BarX

should yield:

data Foo = Bar
               X

that is assume by default that I will be writing arguments of Bar. In this example this doesn't look good, but it seems to make sense in general. For example:

data Foo = Bar Int Char
               X

It would be nice if entering a vertical bar in the setting above was detected and indentation corrected automatically to:

data Foo = Bar Int Char
         | X

Note the space already inserted after the |. Also, in this setting:

data Foo = Bar Int Char
               X

I would expect that repeatedly pressing Tab will cycle me between four indentations:

data Foo = Bar Int Char
X        Y Z   Q

Currently I am cycled only between X and Z.

[gracjan]

Electric behavior for bar comma semicolon is in the plans. Hard to say when we will have energy to do this.

[gracjan]

Note that haskell-indent behaves the same when electric-indent-mode is enabled. Logic what should happen after ENTER is pressed is here:

https://github.com/haskell/haskell-mode/blob/master/haskell-indentation.el#L188

[gracjan]

This is a duplicate of #747.